This points out a problem with convertible reserves for currencies. Whether it is USDT and dollars, or dollars and gold, the only way to be sure that there is enough backing for the value of the currency issued is to take your currency in and trade it for the thing of value that backs it. If you show up to make a trade and the issuer refuses, then there may not be enough dollars or gold to trade.
And if you're going to shlep down to the bank to trade in your dollars for gold (or go online to trade "stablecoins" for the backing fiat currency), then you may as well require your pay be in that form in the first place.